Embodiments of the present invention relate to impact tools for use in drilling operations, and more particularly, to fluid actuated percussive drilling equipment such as used in rock drilling and similar operations.
Down hole well drilling, for oil, gas, or water, requires a specially designed drill apparatus, which can be used in applications where the diameter of the drill body is less than the drill bit diameter. The drill apparatus must provide high energy output, simplicity, and reliability in order to provide economical operation, and must also be able to withstand the abrasive environment as well as the continuous impact loading required for cutting through rock.
Pressurized fluid-actuated impact tools, and in particular pneumatic down-the-hole rock drills of this type, are generally known, as disclosed in U.S. Pat. No. 4,084,646, the disclosure of which is incorporated herein by reference. This patent discloses a drill having only a single moving part and all valving of the pressurized fluid is accomplished by interior and exterior porting on the piston and the casing. In such known drills, the moving part comprises a piston which strikes directly on the percussive bit. The known devices utilize a piston weighing between 45 and 50 pounds which is reciprocated at a frequency of approximately 1,500-1,800 blows per minute by pressurized air, generally provided at 250 to 350 psi. U.S. Pat. No. 5,944,117, the entire contents of which are incorporated by reference herein, also discloses a pressurized fluid-actuated impact tool.
Standard drill bits are conventionally utilized with pistons having internal ports. However, the ports make the piston more susceptible to damage from shock waves disbursed from the cut edges of the hole, causing fatigue and shortening the life of the drill. Solid pistons (i.e., pistons with no internal ports other than a central longitudinal bore) enable the shock waves to be disbursed evenly, but cannot be connected to a standard drill bit. An exhaust tube or foot valve is required to connect the bores of the piston and the drill bit. The foot valve is fragile and susceptible to breakage from stresses, water, and the like. It is therefore desirable to provide a fluid-actuated impact tool that can utilize a solid piston with a standard drill bit.
Further, when the drill bit is located in the hole but is not operating, gravity pulls the drill bit and piston downward, opening a channel for the entrance of water (and all of the sediment and/or debris carried therewith) into the drill. It is therefore desirable to provide a seal within the drill when the drill is not operating to prevent the entrance of water therein to avoid damaging or compromising the tight tolerances of the components therein.